Repeater



1935' A. D. DOWD 2,019,597

REPEATER Filed Aug. 19, 1932 Patented Nov. 5, 1935 UNITED STATES PATENTOFFI' Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application August 19, 1932,Serial No. 629,484

3 Claims.

This invention relates to repeaters for telegraph and similar impulses.

General objects of the invention are to provide simpler and moreeifective repeaters of the type employing two relays.

The invention from one aspect may be viewed as an improvement upon Fig.1 of Patent 1,580,192, issued April 13, 1926 to Fell. In the disclosureof that patent is found a simple type of through repeater provided witha pair of polar relays each having two windings differentiallyconnected. The repeater is connected between two line sections. Aterminal of the first winding of each relay is connected to the linewhile a terminal of the second winding is connected to ground through anartificial line with the apex of the two windings connected to thearmatures of the other relay in each case. When the line is closed bothrelays are energized and the armatures at their marking contacts areconnected to a positive source of potential. When either relay releasesdue to an interruption signal in either line section, the relay in theopposite line section is re.- quired to remain energized in order not tosend a break signal to the sending station. In such case a tendency hasbeen found for the relay to release falsely due to surges in the linewinding under certain line conditions. Since the line sections or loopcircuits to which such repeaters are connected often vary considerablyin length and electrical characteristics, this tendency may becomepronounced and cause the repeaters to operate in an unsatisfactorymanner. Accordingly, it is an object of this invention to provide, inrepeater sets having one pair of relays arrangements for reducing thetendency to operate falsely.

A further object is to improve the operating characteristics of impulserepeaters of the tworelay type so that they will operate successfullywithout adjustment upon lines of large difference.

Other objects and features of the invention will appear more fully fromthe detailed description thereof hereinafter given.

The invention may be more fully understood from the followingdescription together with the accompanying drawing in the figure ofwhich is illustrated one form of embodiment of the invention.

In the drawing are shown two stations Al and A2 interconnected by thelines LI and L2 through a repeater R. The terminal stations compriseprinter magnets, transmitting keys and sending batteries. The repeatercomprises two polarized relays 3 and I3 having their upper or linewindings included in the respective loop circuits including lines LI andL2 and controlled by key K and negative sending battery at stations Aland A2. The lower windings are also connected to the loop circuitsthrough artificial lines to ground. The 5 armatures of relays 3 and I3move between the marking and spacing contacts M and S of said relaysthereby alternately connecting oppositely poled batteries to the line.The relays 3 and I3 may be of the magnetically polarized type or they 10may be polarized electrically; the former type is preferred.

Under normal conditions when no signals are being transmitted, polarizedrelays 3 and I? remain operated due to current through their upper 15line windings. The path for the upper line winding of relay 3 may betraced from negative battery at station Al through compensatingresistances l and 2 of line LI, upper winding of relay 3, choke coil 5,tongue of relay l3 and mark- 20 ing contact M, choke coil 6 to positivebattery. Similarly the path for the upper winding of relay [3 may betraced from negative battery at station A2 through compensatingresistances H and E2 of line L2, upper winding of relay l3, choke coil 5I5, tongue of relay 3 and front contact M, choke coil I6 to positivebattery. The lower windings of relays 3 and [3 are connected from theapexes l and Il, respectively, to ground through the choke coils 9 andI9 and artificial lines AL! and 30 AL2, respectively. The current tostation AI, therefore, divides at apex l of relay 3, part going to theupper winding and part to the lower winding. Similarly, the current tostation A2 divides at apex ll of relay l3, part going to the 35 upperand part to the lower winding.- Since the upper and lower windings aredifferentially connected, the flux in the lower windings opposes theflux in the upper'windings, but does not prevent the relays fromoperating because the current 40 flow through the lower windings isregulated by the artificial line resistances to one-half the currentflow in the upper windings.

When station Al sends a spacing signal by opening break key K the linecurrent drops to zero 45 in the upper winding of relay 3 thus causing itto release assisted by the flux in the lower winding. The tongue ofrelay 3 thus breaks its contact with positive battery and closes contactwith negative battery at contact S. Since station A2 is also 50connected to negative battery the line current through the upper windingof relay l3 drops to a small fraction of its normal value, for example,.005 ampere and transmits the spacing signal to station A2, but relay l3does not release because 55 the flux in the lower winding on negativebattery is now aiding the operation of the relay and it remainsoperated. On closure of the break key K at station Al to send a markingsignal, line current through the upper winding of relay 3 again operatesthe relay to connect positive battery to the line L2 of the station A2.In a similar manner station A2 may send spacing and marking signals tostation Al whereupon relay l3 releases and reoperates in the mannerdescribed for relay 3.' If the key K at station A2 is opened while thekey at station AI opens, no effect would be noted at station AI becausethe current in line L2 is already practically zerodue to negativebattery at the tongue and S contact of relay 3 and relay l3 remainsoperated as previously described. If, however, the key at station A2remains open until the key at station AI is again closed to send amarking signal, relay 3 will reoperate and the positive battery at themarking contact M will reverse the current in the lower marking windingof relay I3 and cause it to release and thereby repeat the break signalfrom station A2 to the station Al. Station Al then cannot send becauseline LI is connected to negative battery at the tongue and S contact ofrelay I3.

The lower windings of relays 3 and I3 are differentially connected withrespect to the upper or line windings and serve a two-fold purpose.Under certain conditions the currents are utilized for holding purposesand under other conditions the currents are utilized for biasingpurposes. The constants of the circuit are so arranged that with thekeys K closed, current of about .060 ampere flows in the upper windingsand a current of about .030 ampere flows in the lower windings. Sincethe pull of the lower windings is opposite in efiect to the pull in theupper windings, the net result is equivalent to a current of .030 amperein a single coil which acts to hold the tongues of the relays to theirmarking contacts M. When no current flows in the upper winding of relay3 as would be the case with key K open at station Al then the lowerwinding will act to move the relay tongue to the opposite contact owingto the pull produced by the current of approximately .035 ampere. RelayI3 operates in the same manner when key K at station A2 is sendingspacing and marking impulses to station AI.

Assuming now that station AI sends a spacing signal by opening key K,current in upper winding of relay 3 falls to zero and the lower windingbecomes effective in moving the tongue of the relay to contact S. At themoment the tongue breaks the circuit with the front or marking contactM, condenser 25 in series with resistance 26 begins charging and has theeffect of prolonging the current flow through choke coil I5 and the twowindings of relay I3. Condenser 25 in this case has an increasedcapacity over that required for contact protection (i. e. spark-killing)thus maintaining a holding current for relay I3 until the tongue ofrelay 3 makes contact with the S contact. At the instant this occurscurrent in the upper winding of relay I3 begins to fall to zero and thepolarity of the lower winding of relay I3 is reversed thus efiectivelymaintaining relay I3 in an operated condition. When station AI sends amarking signal by closing key K, current in the upper winding of reay 3builds up un til it overcomes the pull of the lower winding in theopposite direction and the tongue of the relay starts to open the backor spacing contact S. During the travel of the tongue of relay 3 fromcontact S to the contact M, the lower winding of relay [3 continues toremain energized through the upper winding and line L2 to negativebattery at station A2. The capacity of condenser 21 thus is onlyrequired to be high enough to absorb the spark at contact S. When relay3 finally pulls the tongue over to the marking contact M, the current inthe upper winding of relay I3 is increased to its normal value and thecurrent in the lower winding reverses direction, and building up slowlydoes not cause relay l3 to release because of the main line current inthe upper winding. The sending of spacing and marking signals fromstation A2 acts on relays l3 and 3 in the same manner as described forrelays 3 and I3, respectively, above. The capacity of condenser 2| inthis case is likewise larger than is required for purely contactprotection in order to prolong the current flow in windings of relay 3when relay I3 releases on spacing current from station A2.

Arrangements to prevent radio energy likely to disturb radio receiversin the vicinity of the repeaters may comprise choke coils 5, 6, 9, l0,I5, I6, l9, and 20 which in combination with the condenser-resistanceunits connected across the M and S contacts of relays 3 and I3 serve toreduce radiation from the relay contacts to such an extent that it willnot materially interfere with the operation or radio equipment operatingupon broadcasting or shorter wave lengths that may be located nearby.

In the preferred arrangement compensating line resistances I and II arelocated at the subscribers station and resistances 2 and I2 are locatedat the repeater office. The effect of splitting the resistances in thismanner is to counteract the effect of line capacity and thus make formore uniform operation of the repeater relays.

Summarizing, therefore, it is thought that two distinctive features ofimprovement are found in the present disclosure.

. First, the condenser 25 (the same is true of condenser 2 I) acts tomaintain the operating current conditions in the windings of relay I!while the armature of relay 3 is passing from its marking to its spacingcontact; more accurate repetition of impulses is therefore accomplished.When the armature of relay 3 moves from its spacing to its markingcontact current conditions in the windings of relay l3 are maintainedwithout assistance from condenser 21. It is emphasized that this currentmaintaining effect is independent of spark-killing condensers andrequires for the condensers 25 and 2I a capacity of a greater magnitudethan is employed for spark killing.

A second feature comprises the various choke coils and condenser unitswhich reduce to a large extent the interference of the repeater withsensitive radio sets in the neighborhood by reducing radiation from therelay contacts and/or changing the periodicity of waves or impulsesradiated. This is accomplished without afiecting the reliability of thedevice as a telegraphic repeater.

While the invention has been disclosed in certain specific arrangementswhich are deemed desirable, it is to be understood that it is capable ofembodiment in somewhat modified forms without departing from the scopeof the invention as defined in the appended claims.

For the purpose of the appended claims the relay 3 will be considered asa transmitting relay from line LI to the line L2.

What is claimed is:

1. In a telegraphic repeater, two relays for r peating each way betweentwo lines, a circuit controlled by the armature of each relay extendingthrough a winding of the other to the receiving line, said armature inoperating passing from a contact to another contact over each of whichcurrent flows through the windings of said other relay and a condenserconnected between said armature and contact of sufficient magnitude tomaintain the current flow condition while said armature passes from onecontact to the other, said condenser being of greater capacity than aspark protection condenser for the reasons aforesaid.

2. In a telegraph repeater, two relays for repeating each way betweentwo lines, a circuit controlled by the armature of each relay extendingthrough a winding of the other to the receiving line, said armature inoperating passing from a marking contact to a spacing contact, sourcesof difierent polarity connected to said contacts and a connection fromsaid armature over which current flows through windings of said otherrelay, and a path including a condenser connected between said armatureand said marking contact, said condenser being of sufiicient magnitudeto maintain the current flow condition previously existing while saidarmature passes from said marking contact to said spacing contact. 10

than the condenser connected between said arma- 15 ture and said markingcontact.

ANDREW D. DOWD.

